This invention relates to a multiple contact connector for a printed circuit board, the connector comprising a plurality of contact springs for contacting conductor strips provided at an edge portion of the circuit board.
Printed circuit boards consisting of a ceramic substrate have tolerances in length and thickness caused in the production process. Particularly, circuit boards of this type are not entirely plane but are slightly curved. In order to ensure safe contacts even under critical tolerances in thickness, the contact springs are selected to exert relatively high contact pressures on the circuit board. As a result, when the circuit board is inserted into the connector, high friction occurs on at least some of the conductor strips over a long distance, which may cause damage to the conductor strips after several inserting actions. Moreover, the edge of such circuit board is mostly very sharp as a consequence of the production process so that the precious metal layer by which the contact portions of the contact springs are covered is quickly chafed with the result that safe contact is no longer ensured when the circuit board has been exchanged a number of times.
Furthermore, modern circuitry requires high packing density according to which a great number of circuits are accommodated on a relatively small circuit board, for instance by employing thin film technology. This results in a great number of conductor strips formed at the edge of the circuit board which conductor strips are rather narrow and prone to friction wear.
Since as many conductor strips as possible are to be accommodated at small distances along the edge of the circuit board and since, on the other hand, the tolerances in the length of the board and thus the relative position of the conductor strips jeopardize a safe contacting, it is necessary for the circuit board to be inserted into the connector in such a manner that there is at least one fixed reference point from which the position of each conductor strip may be determined.
As an additional difficulty, the tolerance in the length of the circuit board caused by contraction in the production process varies from one manufacturer to the other, so that it is often impossible to change the circuit boards as desired.
For overcoming the above disadvantages, a plug-in connection is known in which the printed circuit board has at one edge metal lugs forming the terminals of the circuit. The multiple-contact connector includes a number of pairs of pins. When the circuit board is inserted into the housing, the pins are forced into the metal lugs from both sides of the circuit board thereby making the contact.
Another plug-in connection has been suggested in which a contact pressure is produced or released by a mechanism during inserting or removing the circuit board. An eccentric cam portion is disposed between the contact springs, by means of which the contact springs may be spread apart while inserting or removing the circuit board.
In another similar plug-in connection, the contacts between the circuit board and the contact springs are made by a cam switch provided in a housing on one side of the contact springs, which cam switch is rotated manually upon inserting the circuit board so as to force the contact springs against the conductor strip.
In a further known plug-in connection, the contact spring element is formed and mounted in a housing in such a way that the circuit board is brought into contact engagement by being deformed beyond a flexing point, the kinematic action being similar to that of a toggle joint. The actuating force required for the plug-in action is transmitted through a flexible coupling rather than directly from one part to another. The actuating force which acts originally only in the plugging direction, rises from zero to a maximum and then falls back to zero. At the maximum of the actuating force which firstly serves to deform the contact element, the flexing point is reached at which the contact of both parts is made. When the flexing point has been passed, the actuating force falls back to zero while the contact force is only slightly reduced.
The above known plug-in connections have the disadvantage that the spreading means require additional space, which is aggravated by the fact that the spreading means must be readily accessible for manual operation. As a further disadvantage, foreign matter that may affect the contacts is not removed by any wiping movement or small friction occurring over a small distance during inserting of the circuit board.
In a further known plug-in connection, forked contact springs are mounted in a housing for receiving a retaining bar inserted into a recess in the lower portion of the contact springs. Circuit boards of variable thickness can be accommodated by changing the retaining bars. Brackets are formed integrally at the sides of the retaining bar to compensate for different lengths of the circuit boards. While tolerances in thickness and length between individual circuit boards may be compensated for with such retaining bar, the fact that almost every circuit board is not totally plane but at least slightly curved, is still left out of consideration. As an additional disadvantage, a great number of different retaining bars must be available to be employed in accordance with the dimensions of the individual circuit board.
It is an object of the present invention to provide a multiple-contact connector for a printed circuit board which is free from the above disadvantages.
Another object of the invention is to provide a connector of the said type which allows easy and rapid inserting of a printed circuit board into the connector for making the required contacts.
A further object of the invention is the provision of a multiple-contact connector in which a printed circuit board automatically assumes an exact position with respect to the connector in a final locked position.
It is still a further object of the invention to make available a multiple-contact connector in which the circuit board is contacted with a small frictional movement occurring during inserting the contact board.